The invention relates to a plug for fastening to hollow building materials and to solid building materials, having the features of the preamble of claim 1. Hollow building materials are understood herein to be, for example, hollow block bricks or panels behind which there is a cavity. Solid building materials are understood to be, for example, concrete or the like.
Such plugs are known per se. They are usually made of plastics material and, in a middle region, have expansion limbs extending longitudinally and separated from one another by slits. The expansion limbs are connected to one another at a rear end by a sleeve-like plug end and at a front end by a sleeve-like plug tip. An expansion screw can be pushed through the sleeve-like plug end and screwed into the plug tip. For the purpose of fastening the plug in a solid building material, the plug is inserted in a hole drilled in the solid building material and an expansion screw is screwed into the plug. The expansion screw pushes the expansion limbs apart, that is to say the expansion screw expands the expansion limbs and, as a result, anchors the plug in the hole drilled in the solid building material.
In a hollow building material or in a panel, the plug is pushed through a drilled hole so that its sleeve-like plug end is located in the hollow building material. An expansion screw is then pushed through the plug end, guided through between the expansion limbs and screwed into the plug end. Screwing the expansion screw into the plug tip causes the plug tip to move towards the plug end, in the process of which the expansion limbs are expanded. Two possibilities for expansion are known per se. The first is that the expansion limbs bend outwards as the plug tip comes closer to the plug end and, as a result, grip behind the hollow building material in positive manner. The other possibility is that, when the expansion screw is being screwed in, the plug tip twists relative to the plug end, as a result of which the expansion limbs are wound around one another and form a knot-like structure that grips behind the hollow building material.
The known plugs have the disadvantage of poor screw guidance; when being screwed in, the expansion screw can emerge to the side through the slits between the expansion limbs. A further disadvantage of the known plugs is their low torsional rigidity, which results in resilient twisting of the plug tip relative to the plug end when the expansion screw is being screwed in. When the expansion screw is being screwed in by hand, the resilient twisting of the plug tip with respect to the plug end causes the plug tip, together with the expansion screw screwed into it, to rotate back again when a screwdriver is released for xe2x80x9cgrip changingxe2x80x9d. The consequence thereof is that the expansion screw can be screwed into the plug by hand only poorly.
The invention is based on the problem of avoiding the disadvantages mentioned above.
The problem is solved in accordance with the invention. In the plug according in which the expansion limbs are connected to one another in a peripheral direction by an expandable material. For the purpose of expandability, the material can be thinly formed and/or can be corrugated in the peripheral direction of the plug. When the plug is made from plastics material, the expandable material is preferably integral with the expansion limbs and consequently is made from the same plastics material as the rest of the plug. The expandable material in that case is preferably thinly formed as a plastic skin. As a result of the connection of the expansion limbs in the peripheral direction, the plug according to the invention is shaped like a sleeve which is closed in the peripheral direction even in the region of the expansion limbs. As a result, good guidance of the expansion screw is achieved and the expansion screw is preventing from emerging through the side of the plug between the expansion limbs, even when the expansion screw is subjected to a transverse load. A further advantage of connecting the expansion limbs in a peripheral direction is an increase in the torsional rigidity of the plug. The increased torsional rigidity firstly has the advantage that, when the expansion screw is being screwed in, the plug tip rotates together with the screw to a lesser extent, as a result of which the expansion screw can be better screwed into the plug tip. Furthermore, the increased torsional rigidity has the advantage that, when the screwing torque is released, for example when changing grip on a screwdriver, the plug tip rotates back less. As a result, the expansion screw is easier to screw into the plug, especially when it is being screwed in by hand. In addition, the plug according to the invention has the advantage that, when the expansion screw is being screwed in, there is a less pronounced drop in torque after expansion in a hollow building material has begun. In the case of the known expansion plugs, there is a marked drop in the torque once the expansion limbs have begun to bend out or wind around one another when the plug is being fastened to a hollow building material. As a result of the increased rigidity of the plug according to the invention caused by connecting its expansion limbs in a peripheral direction, that effect is, at least, smaller in is disadvantageous because it gives the false impression that the expansion screw or the plug have come away as a result of excessive force and consequently do not have a firm seating in the hollow building material.
In an embodiment of the invention, the sleeve-like plug end has a larger transverse dimension than the rest of the plug. This embodiment has the purpose of providing the plug with a good seating in a hollow or panel-type building material, in which essentially only the sleeve-like plug end of the plug is accommodated within the drilled hole and the rest of the plug is in a hollow space.
In an embodiment of the invention, a cross-section of the sleeve-like plug end has a sawtooth-like contour. This means that the plug end has radial surfaces, from the outer edge of which a contour line of the plug end extends inwards to the next radial surface in the manner of a helix contrary to the direction in which the expansion screw is screwed in. The radial surfaces are therefore oriented in the direction in which the expansion screw is screwed in. In soft building materials, they form a kind of abutment that presses into the building material and forms an anti-rotation means, which holds the plug in the building material so that it does not rotate when the expansion screw is being screwed in. Of course, the radial surfaces need not be oriented exactly radially. Especially together with the plug end having a larger cross-section compared to the rest of the plug, the sawtooth-like arrangement of the contour of the plug end provides a good anti-rotation means in soft building materials because, when the plug is introduced into a hole drilled in a soft building material, the plug end having a relatively large transverse dimension so compresses the building material in a region surrounding the plug end that the radial surfaces digging into the building material gain a good hold in the building material.
In an embodiment of the invention, the sleeve-like plug tip is provided with angled, for example V-shaped, slits, the corner (point) or tip of the slits pointing preferably towards the front or towards the rear end of the plug. As a result of being angled, the slits have one leg that has a pitch in the same direction as the pitch of the thread on the expansion screw and another leg that has a pitch in the opposite direction. The pitch of the slits in the plug tip can differ from the pitch of the thread on the expansion screw, it is merely their direction that is the same or opposite. The legs of the angled slits whose pitch is in the same direction as the thread pitch on the expansion screw serve to engage the turns of thread on the expansion screw; they bring about good adaptation to different screw diameters. The angled slits bring about reliable engagement of an expansion screw of small diameter without the expansion screw coming out of the plug tip when the expansion screw is tightened. At the same time, the angled slits avoid a large increase in torque when screwing in an expansion screw having a large screw diameter.
The legs of the angled slits whose pitch is in the opposite direction to the pitch of the thread on the expansion screw bring about axial expandability of the plug tip, as a result of which the axial spacing of angled slits provided in axial succession on the plug tip changes. By that means, adaptation to different pitches of thread on expansion screws is achieved.
In an embodiment of the invention, the plug has, within the sleeve-like plug tip, a screw channel for the expansion screw, which screw channel has a cross-section that is other than circular in shape. The screw channel within the plug tip therefore has different transverse dimensions in different directions. This measure also serves to adapt the plug to different diameters of expansion screw. In a development, the screw channel within the plug tip has a flat, for example slot-shaped, screw channel. The screw channel within the plug tip can also have the shape of two slots that cross one another.